As the death toll climbs to nearly 900, concerns mount that the epidemic is spreading faster than efforts to contain it.

The death toll from the Ebola virus outbreak in West Africa has reached 887, that's according to the World Health Organisation (WHO).

The organisation's director-general, Margaret Chan, said: "If the situation continues to deteriorate, the consequences can be catastrophic in terms of lost lives, but also severe socio-economic disruption and a high risk of spread to other countries. This outbreak is moving faster than our efforts to control it."

And now the World Bank has pledged up to $200m in emergency funding to help fight the virus in West Africa. The African Development Bank has promised about $60m.

The money will be go to Guinea, Liberia and Sierra Leone - the three West African countries most affected.

But how should the money be used? And what are the challenges of containing the spread of this epidemic?